Pre and postmenopausal women are being fed varying concentrations of soy derived isoflavones. The relationship between the dose of isoflavones ingested and the amount of isoflavones and their bacterial metabolites excreted in the urine is being measured. The levels of isoflavones and their metabolites in the plasma are being measured and the relationship between the amount of isoflavones consumed and the urinary and plasma levels is being defined. In addition, the effect of isoflavones and their dose relationship to endogenous urinary and circulating estrogens is being determined.